package jjn.acwing;

import java.util.Scanner;

/**
 * @author Jiang Jining
 * @since 2023-07-19 19:39
 */
public class Acwing608 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int a = scanner.nextInt();
        int b = scanner.nextInt();
        int c = scanner.nextInt();
        int d = scanner.nextInt();
        int res = (a * b) - (c * d);
        System.out.printf("DIFERENCA = %d", res);
    }
}
